As mammals age there is a tendency for them to become fat. The liver is the major site of both fatty acid and cholesterol synthesis in rat. The effect of aging on the rates of fatty acid and cholesterol synthesis by rat liver will be investigated. The composition of the end products and the rates of de novo synthesis and chain elongation of fatty acids will be studied. These parameters will be measured on groups of male and female rats, both in vivo and in the perfused liver, using rats aged from 3 to 24, and, if possible, 30 months. It is hoped that the research project will add to our understanding of the molecular and cellular basis of aging.